mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2025-10-26 02:20:20 -04:00
5ac886855d
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6437 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
126 lines
5.9 KiB
HTML
Executable File
126 lines
5.9 KiB
HTML
Executable File
<HTML><HEAD>
|
|
|
|
<TITLE> Notes on Modifying the LDPC Programs </TITLE>
|
|
|
|
</HEAD><BODY>
|
|
|
|
|
|
<H1> Notes on Modifying the LDPC Programs </H1>
|
|
|
|
<P>Here are a few notes on how to modify the programs to add new types of
|
|
channel, new decoding procedures, etc. You should also look at the <A
|
|
HREF="modules.html">module documentation</A>.
|
|
|
|
<H2> Adding a new type of channel </H2>
|
|
|
|
<P>Channels are involved in two programs:
|
|
<A HREF="channel.html#transmit"><B>transmit</B></A> and
|
|
<A HREF="decoding.html#decode"><B>decode</B></A>.
|
|
Adding another type of memoryless channel should be straightforward.
|
|
Adding a channel with memory may involve more work. Here are the
|
|
steps needed if no major reorganizations are required:
|
|
<OL>
|
|
<LI> Decide on a syntax for specifying the new channel type and its
|
|
parameters, and on an internal name for the channel type. Add
|
|
the internal name as a possibility in the enumerated <TT>channel_type</TT>
|
|
declared in <A HREF="channel.h"><TT>channel.h</TT></A>. You
|
|
may also need to declare new global variables to store parameters of
|
|
the channel in <A HREF="channel.h"><TT>channel.h</TT></A> and
|
|
<A HREF="channel.c"><TT>channel.c</TT></A>.
|
|
<LI> Modify the <TT>channel_parse</TT> and
|
|
<TT>channel_usage</TT> procedures in
|
|
<A HREF="channel.c"><TT>channel.c</TT></A> to
|
|
parse the specification of the new channel and display an appropriate
|
|
usage message.
|
|
<LI> Decide on how the new channel's output is represented in a file
|
|
(eg, for an erasure channel, what the symbol for an erasure is), and
|
|
update <A HREF="transmit.c"><TT>transmit.c</TT></A> to write the
|
|
new channel's output for each transmitted bit, after randomly generating
|
|
any noise (see
|
|
the <A HREF="rand.html">documentation on random number generation</A>).
|
|
<LI> Modify <A HREF="decode.c"><TT>decode.c</TT></A> in three places to
|
|
accommodate the new channel. The three sections of code to modify
|
|
allocate space for data from the channel, read data from the channel,
|
|
and set likelihood ratios based on the data read. The setting of
|
|
likelihood ratios is based on the assumption that the channel is
|
|
memoryless (ie, data received for different bits is independent).
|
|
Adding a channel with memory would require changing this assumption,
|
|
which would involve modifications to the decoding procedures too.
|
|
<LI> Document the new channel type in <A HREF="channel.html">channel.html</A>
|
|
and <A HREF="decoding.html">decoding.html</A>.
|
|
</OL>
|
|
|
|
<H2> Adding a new decoding procedure </H2>
|
|
|
|
A new decoding method can be implemented as follows:
|
|
<OL>
|
|
<LI> Decide on a syntax for specifying the method and its parameters,
|
|
using the trailing arguments to the
|
|
<A HREF="decoding.html#decode"><TT>decode</TT></A> program. Pick an
|
|
internal name for the method, and add it as a possibility in the
|
|
enumerated <TT>decoding_method</TT> type in
|
|
<A HREF="dec.h"><TT>dec.h</TT></A>. You may also need to declare
|
|
new variables for the method's parameters in
|
|
<A HREF="dec.h"><TT>dec.h</TT></A> and <A HREF="dec.c"><TT>dec.c</TT></A>.
|
|
<LI> Modify the argument parsing code in
|
|
<A HREF="decode.c"><TT>decode.c</TT></A>
|
|
to handle specifications of the new method, and change the <TT>usage</TT>
|
|
procedure to display the syntax for specifying the new method.
|
|
<LI> Write a setup procedure for your decoding method, putting it in
|
|
<A HREF="dec.c"><TT>dec.c</TT></A>, with a declaration in
|
|
<A HREF="dec.h"><TT>dec.h</TT></A>. At a minimum, this procedure
|
|
should print headers for the table of detailed decoding information
|
|
when the <B>-T</B> option was specified.
|
|
<LI> Write a decode procedure implementing your method, putting it in
|
|
<A HREF="dec.c"><TT>dec.c</TT></A>, with a declaration in
|
|
<A HREF="dec.h"><TT>dec.h</TT></A>. This procedure should output
|
|
detailed trace information when the <B>-T</B> option was specified.
|
|
<LI> Modify <A HREF="decode.c"><TT>decode.c</TT></A> in the appropriate
|
|
places to call the setup procedure and the decode procedure you wrote.
|
|
<LI> Document the new decoding method in
|
|
<A HREF="decoding.html">decoding.html</A> and
|
|
<A HREF="decode-detail.html">decode-detail.html</A>.
|
|
</OL>
|
|
|
|
<H2> Adding a new method of making a low-density parity-check matrix </H2>
|
|
|
|
<P>The <A HREF="pchk.html#make-ldpc"><B>make-ldpc</B></A> program can be
|
|
changed to add a new method for generating a LDPC code by modifying
|
|
<A HREF="make-ldpc.c"><TT>make-ldpc.c</TT></A>. A radically different
|
|
method might better be implemented by writing a new program of similar
|
|
structure.
|
|
|
|
|
|
<H2> Adding a new encoding method </H2>
|
|
|
|
<P>A new heuristic for finding a sparse LU decomposition can be
|
|
implemented by changing <A HREF="make-gen.c">make-gen.c</A> to allow
|
|
the new heuristic to be specified on the command line, changing the <A
|
|
HREF="mod2sparse.html#decomp"><B>mod2sparse_decomp</B></A> procedure
|
|
in <A HREF="mod2sparse.c"><TT>mod2sparse.c</TT></A> to implement the
|
|
heuristic, and documenting the new heuristic in <A
|
|
HREF="encoding.html">encoding.html</A>, <A
|
|
HREF="sparse-LU.html">sparse-LU.html</A>, and <A
|
|
HREF="mod2sparse.html">mod2sparse.html</A>.
|
|
|
|
<P>To implement a completely new encoding method, you will first need
|
|
to define a new file format for a generator matrix, modify <A
|
|
HREF="make-gen.c">make-gen.c</A> appropriately to write out this new
|
|
format, and modify the <TT>read_gen</TT> procedure in <A
|
|
HREF="rcode.c"><TT>rcode.c</TT></A> to read this format. You will
|
|
need to implement the new method in a procedure in <A
|
|
HREF="enc.c">enc.c</A>, and modify <A HREF="encode.c">encode.c</A> so
|
|
that it will call this new procedure when the new method is used. The
|
|
<TT>enum_decode</TT> procedure in <A HREF="dec.c">dec.c</A> will also
|
|
need to be modified so it can call the new encoding method. Finally,
|
|
you should document the new method in <A
|
|
HREF="encoding.html">encoding.html</A>
|
|
|
|
<P>
|
|
|
|
<HR>
|
|
|
|
<A HREF="index.html">Back to index for LDPC software</A>
|
|
|
|
</BODY></HTML>
|